The invention relates to a device comprising a symmetrical amplifier which has, inter alia, at least one input terminal for receiving a voltage to be amplified, a pair of output terminals for producing a symmetrical amplified voltage, and a symmetrical amplifier circuit having inputs for being connected to said input terminal, and outputs for being connected to said output terminals, and also a gain control for receiving a gain control signal.
The invention finds interesting applications notably in the field of optical fibers which transmit at a very rate (xcx9c10 Gbits/s). In this field a transformation is to be provided which adapts the signals transported by the optical fiber to signals intended for a line of electric wires. This transformation implies symmetrical types of amplifications. Reference may be made to the instructions for use of the component TZA3013A manufactured by Philips. To obtain a proper conversion of the signals for said electric wire line, it is known practice that the amplitude of the signals is to be properly regulated. A good quality for this regulation is hard to obtain because it is difficult to have a good measurement of the amplitude of the signals on the output of the symmetrical amplifier at the working frequencies considered, this measurement being affected by offset voltage variations which are due to inter alia thermal drift and ageing.
The present invention proposes a device of the type mentioned in the opening paragraph which permits to have a constant amplitude gain of the signals intended for the electric wires even if a variation of the offset voltage occurs.
For this purpose such a device is characterized in that said amplifier furthermore includes a circuit for measuring the amplitude of signals to produce said gain control signal, which circuit is formed by amplitude detectors of the same type, connected to produce measurements which represent the amplitude of electrical magnitudes at said output terminals.
The inventive idea comprises the use of detectors of the same type, for example, peak detectors for measuring the amplitude of the signals on the symmetrical outputs of the amplifier and not by a peak detector for an output and a valley detector. These detectors involve transistors of different types with which it is difficult to match the electrical characteristics.
These and other aspects of the invention are apparent from and will be elucidated, by way of non-limitative example, with reference to the embodiments described hereinafter.